The Sky Blues made it three wins on the bounce and nine unbeaten in League One on Tuesday night, with three points against Portsmouth.
City went into the game on the back of victories against Bristol Rovers and Bolton Wanderers and that would be extended to three against Portsmouth.
Matty Godden came off of the bench in the 82nd minute and then in the 84th he latched onto Callum O'Hare's through ball and finished superbly past Alex Bass to make it 1-0.